A guide would take most of the fun out of this game, imo. The point is to try stuff and see what new progression paths you can unlock.
If you feel like you're stuck in Willowbrook, I'd recommend trying to achieve the maximum mastery status in each activity (it's not really a maximum as the mastery number can still go up, but the game will tell you there is nothing more to discover by advancing it) or trying to defeat all enemies in the exploration areas.
Also make sure you're buying the permanent upgrades from the shop, as those will be required for meaningful progress across reincarnations.